Electric heating pads are known which comprise a continuous resistance heating wire sandwiched between two insulating sheets typically of plastic. The wire zig-zags back and forth transversely of the sheets in longitudinally spaced runs, typically in the manner of a flat coil.
Past methods for forming the wire into the transverse runs have not proven satisfactory. In methods such as that taught by U.S. Pat. No. 4,613,390 to Mela and U.S. Pat. No. 2,548,467 to Crise, the zig-zagging wire is formed and laid onto one sheet before a second sheet is applied. These methods have the major disadvantage that the wires move and lose their desired relative positioning. The present applicant has appreciated the disadvantage that prior art methods do not maintain the wire tensioned substantially until the time when the wires are secured between the sheets. This has the disadvantage that the wires can become improperly located and spaced and slack in the wires, particularly with the expansion on heating of the wire can cause an increased localized heating leading to failure of the wire or seats.
Most prior art methods for forming heater pads fail to provide a simplified system for electrically coupling the heater wire to an electrical source.